1. Field of the Invention
The present invention relates to methods for annealing a semiconductor device, and particularly to an annealing apparatus used in high intensity light sources, annealing methods and manufacturing methods of semiconductor devices.
2. Description of the Related Art
It is possible to realize improvements in semiconductor device performance-enhancing Large Scale Integration (LSI) and the like by increasing integration, or put more plainly, by miniaturization of the elements that build up a semiconductor device. Thus, LSI is becoming increasingly large-scale while miniaturization of elements such as metal-oxide-semiconductor (MOS) transistors is being taken to a whole new level. Along with the miniaturization of composing elements, parasitic resistance and short channel effects on MOS transistors and the like, increase. Thus, there is increased importance placed on the formation of low resistance layers and shallow pn junctions.
For forming a shallow pn junction with a thickness of or below twenty nm, a thin impurity doped region is formed using an ion implantation in a semiconductor substrate with low acceleration energy. The impurities doped in the semiconductor substrate are activated by an annealing process, thus forming a shallow impurity diffusion region. In order to lower layer resistance of an impurity diffusion region it is necessary to perform activation annealing of the impurities at a high temperature.
However, the diffusion coefficients of p-type impurity such as boron (B), and n-type impurity such as phosphorus (P) or arsenic (As), in the crystal of the silicon substrate, are large. In the time needed to perform rapid thermal annealing (RTA) using current halogen lamps, impurities diffuse to both the interior and exterior of a semiconductor substrate. As a result, it is impossible to form a shallow impurity diffusion region having a high concentration of impurities on the semiconductor substrate. Also, it becomes impossible to activate a high concentration of impurities if the temperature of the RTA process is lowered in order to control the diffusion of the impurities. In this manner, it is difficult to form a shallow impurity diffusion region having low resistance and a high concentration of activated impurities.
Recently a pulse light annealing method by the use of a pulse light source such as a flash lamp and a YAG laser, which can instantly supply the energy essential to impurity activation, is being tested as a solution to the RTA problem. A xenon (Xe) flash lamp has a quartz glass tube filled with Xe gas, in which electrical charges stored in capacitors and the like, are instantaneously discharged. As a result, it becomes possible to emit a high intensity white light within a range of several hundred μs to several hundred ms for instance. It is possible to attain the heat energy required for impurity activation in the instantaneous heating of a semiconductor substrate absorbing flash lamp light. Therefore, it becomes possible to activate a high concentration of impurities while leaving the concentration profile of the impurities implanted into the semiconductor substrate virtually unchanged.
However, in using flash lamp annealing, irradiation energy above 20 J/cm2 is essential to ensure a sufficiently uniform activation of impurities at a high concentration, which would lead to a sudden temperature increase on the semiconductor substrate. As a result, there occurs a temperature difference in between a top surface and a bottom surface of the semiconductor substrate, which raises the amount of thermal stress in the interior of the semiconductor substrate. Thermal stress causes crystal defects such as slips and dislocations. The presence of crystal defects makes it easy for damage to occur on semiconductor substrate, leading to decreases in production yield. Thus, it is difficult to perform annealing with flash lamp annealing processes while suppressing the generation of crystal defects generated on semiconductor substrate.